Dinoflagellates are a group of microscopic
one-celled microorganisms. Most are free swimming and are plant-like,
that is, they have the ability to obtain energy by photosynthesis.
A natural part of the environment, dinoflagellates are nontoxic
organisms.

Pfiesteria piscicida, however,
is an exception to that rule.Although it is classified
as a dinoflagellate, it is toxic and can be both plant-like by
performing photosynthesis and animal-like by consuming other organisms.

Although believed to have been in the environment
for millions of years (http://www.epa.gov/region03/r3press/pr97-369.htm),
Pfiesteria piscicida was only recently discovered. In 1988,
Dr. JoAnn Burkholder, an aquatic ecologist at North Carolina State
University, discovered the organism, and declared it a new species
in a new genus and a new family in the order Dinamoebales. Burkholder
and her associates named the new organism Pfiesteria after
the late Dr. Lois Pfiester, a researcher of dinoflagellates. The
"piscicida" part translates to "fish killer."

Burkholder theorizes that Pfiesteria piscicida
has always been naturally present in the estuaries and tidal
rivers of North Carolina, yet only in the last decade has something
caused it to morph into a toxic fish killer (Barker, 1997). Since
its discovery ten years ago, Pfiesteria piscicida has killed
more than one billion fish (http://www.epa.gov/region03/r3lib/inthenews/archivol.htm).

Although Pfiesteria piscicida has been
blamed for the deaths of so many fish, it is only a small organism.
Throughout the course of its 24 different stages of life, Pfiesteria
piscicida ranges in size from 5 to 450 micrometers (http://www2.ncsu.edu/unity/lockers/project/aquatic_botany/pfiest.html
); several of these stages may produce toxins. Click here to see some Pfiesteria piscicida photos.

Pfiesteria piscicida in
its nontoxic forms is quite harmless; it may masquerade as a plant
and appear to photosynthesize, or it may feed on bacteria and
algae. In the presence of fish excreta and secretions, however,
it is stimulated to metamorphose into a killer. Once triggered,
Pfiesteria piscicida emits a neurotoxin into the water
which subdues the fish and eats through their skin. Pfiesteria
piscicida then feeds on the weak and exposed skin, blood,
and tissue. The fish eventually die not by the invasion of Pfiesteria
piscicida, but by suffocation (the toxins cause paralyzation
of muscles) or by infection (bacteria and foreign objects can
enter the fish through the lesions). After the fish die, the dinoflagellates
may continue to feed on the fish or change forms and disappear,
leaving as the only evidence of its presence open, quarter-sized
lesions on the fish carcasses (http://www2.ncsu.edu/unity/lockers/project/aquatic_botany/pfiest.html
). Click here to see some lesions caused by Pfiesteria
piscicida.

During a fish kill caused by Pfiesteria
piscicida, fish exhibit peculiar behavior. They may swim abnormally,
become disoriented, beach themselves, or hover near the surface
of the water (http://www.dnrec.state.de.us/tpff1.htm). Fifteen
minutes is long enough for Pfiesteriapiscicida to
complete the process of killing a fish (Hager, 1997), therefore,
toxic outbreaks of Pfiesteria piscicida are altogether
very short, normally lasting for the duration of only a few hours.
Fish may continue to develop lesions or even die for days or weeks
afterward, however, once weakened by the toxins (http://www.dnr.state.md.us/pfiesteria/facts.html).

Pfiesteria piscicida has
been busy killing fish when the conditions are right for the past
several years. This year, however, it has not been as active as
in the past. Researchers hypothesize that Pfiesteria piscicida
took a break after storms stirred waters and spread thepopulations, thus making the dinoflagellates less concentrated
and less aggressive.